1. Field of the Invention
The present invention relates in general to aftertreatment devices for internal combustion engines, and more specifically, to high efficiency compression ignition after-treatment devices for combined use with lean-burn combustion systems and three-way catalysts.
2. Description of Related Art
The efficiency, power and emissions characteristics of modern, reciprocating engines are a very strong function of their combustion systems. Two primary combustion system types are in common use. Of these, the most common is the spark-ignited, Otto-cycle engine, which derives its output power from the combustion of a premixed, fuel-air-dilutent charge by a propagating flame within the combustion chamber. Spark ignition engines generally suffer from low thermal efficiencies at light-to-part load, due primarily to the necessity of throttling the airflow through the engine to provide a means of load control.
Additionally, the full-load efficiency and power of these engines suffer due to engine design and control limitations brought about by the possibility of high-load knock, or auto-ignition, of the combustible gases within the combustion chamber. The compression ratio of these engines is lower than the optimum value for efficiency to avoid the knock problem. Further, the ignition timing for the combustion process is retarded from optimal values for efficiency, to avoid knock, and reduce NOx emissions. Increases in the overall efficiency of these engines have been accomplished utilizing lean-burn strategies with turbocharging. However, the knock problem persists and continues to limit the maximum efficiencies of these engines. In addition, exhaust NOx reduction strategies such as timing retard, exhaust gas recirculation, lean-NOx catalysts, and selective catalytic reduction (SCR), lead to further decreases in overall engine efficiency.
The second conventional, predominant combustion system utilizes the diesel-cycle, which derives its power from compression ignition and diffusion burning of a fuel spray injected directly into a mixture of air and dilutent gases. Although the diesel engine does not suffer from knock problems, the maximum fuel-to-air ratio is limited by the production of exhausted particulates. Because the diesel combustion flame bums at nearly stoichiometric proportions, NOx production is high. Exhaust gas recirculation and late injection timing have been used to control in-cylinder NOx formation, but future NOx regulations may require additional NOx reduction strategies such as SCR or use of a lean-NOx catalyst. Legal restrictions on exhaust gas particulate levels may require particulate aftertreatment devices, such as traps or particulate filters.
U.S. Pat. No. 4,793,135, to Obstfelder et al., which is incorporated herein by references, describes the use of separate combustion systems, in parallel, in the same engine. In one of the described embodiments, one of the combustion systems operates on the Otto, or spark ignition principle, whereas the other combustion system operates on a compression, or auto-ignition principle. The two combustion systems operate independently of one another. The separate exhaust gases from both systems are commingled in a mixer whereat, by mixing, the mixed gas is hopefully detoxified with respect to compounds that are undesirable to downstream catalysts. In this parallel arrangement, the separate combustion systems are regulated in order to generate the main toxic components, carbon monoxide and nitrogen oxides at a precise ratio, one with the other. This regulation inhibits operating the engine at its most efficient load/RPM conditions because spark ignition systems generally operate efficiently at a higher rpm and lower load than compression ignition systems.
A need has arisen for combustion system to overcome the problems associated with the above-described parallel combustion system.
In an embodiment of the present invention, a high efficiency compression ignition after-treatment system of a combustion engine may comprise a first combustion chamber adapted to reciprocatably receive a first piston assembly; a second combustion chamber adapted to reciprocatably receive a second piston assembly; and an air inlet passage connected to the first combustion chamber; a combustion exhaust passage connected to the first combustion chamber at a first end, and connected to the second combustion chamber at a second end. The system further comprises a fuel injector in fluid communication with the second combustion chamber; at least one fuel passage in fluid communication with the fuel injector; at least one fuel passage in fluid communication with the first combustion chamber; and a processed exhaust gas passage having a first end and a second end. The first end of the processed exhaust gas passage is connected to the second combustion chamber. A three-way catalyst has an inlet coupled to the second end of the processed exhaust gas passage, and an exhaust gas oxygen sensor is connected to the processed exhaust gas passage between the first end and the second end of the processed exhaust gas passage. A fuel controller is coupled to the fuel injector and the exhaust gas oxygen sensor, wherein the fuel controller controls delivery of fuel through the fuel injector in fluid communication with the second combustion chamber in response to a receiving signal from at least said exhaust gas oxygen sensor, and an exhaust gas passage is coupled to an outlet of the three-way catalyst.
In another embodiment of the present invention, the first piston assembly of the system further may comprise a first piston, a first arm secured to the first piston at a first end of the arm, a first crankshaft secured to the arm at a second end of the first arm. The first crankshaft has means for driving the first crankshaft attached to a first end of the first crankshaft.
In yet another embodiment of the present invention, the second piston assembly of the system further may comprise a second piston, a second arm secured to the second piston at a first end of the second arm, a first crankshaft secured to the second arm at a second end of the second arm. The second crankshaft has means for driving the second crankshaft attached to a first end of the second crankshaft.
In still another embodiment of the present invention, the means for driving the first crankshaft is a first pulley, and the means for driving the second crankshaft is a second pulley. A pulley belt may be connected to the first pulley and the second pulley to secure the first piston assembly and the second piston assembly in a rotational relationship. Alternatively, the means for driving the first crankshaft is a first gear, and the means for driving the second crankshaft is a second gear. A chain drive may be connected to the first gear and the second gear to secure the first piston assembly and the second piston assembly in a rotational relationship. In yet another alternative, the system further may comprise a drive shaft equipped with gear teeth at each end of said drive shaft to engage the first gear and the second gear to secure the first piston assembly and the second piston assembly in a rotational relationship.
In yet a further embodiment, the system may comprise at least one spark source connected to the first combustion chamber for spark ignition of a fuel/air mixture in the first combustion chamber during a combustion cycle. In an alternative to this embodiment, the first combustion chamber may be adapted for compression ignition of a fuel/air mixture.
In another embodiment, the invention is a method for efficiently processing exhaust gases from a lean-burn combustion system. The method may comprise the steps of receiving exhaust gases into a combustion chamber; determining an amount of fuel to be injected by a fuel controller into the combustion chamber; and injecting the amount of fuel into the combustion chamber and recombusting the fuel and the exhaust gases therein. The method also comprises the steps of delivering the recombusted exhaust to a combustion exhaust passage; detecting a composition of the recombusted exhaust in the combustion exhaust passage; transmitting the detected composition to the fuel controller; and adjusting the amount of fuel to be injected into the combustion chamber.
The method of this invention further may comprise the steps of delivering the recombusted exhaust to a catalyst and catalyzing said recombusted exhaust. Finally, the method may comprise the step of delivering the catalyzed exhaust to the environment.